[PATCH 5.10 276/406] printk: ringbuffer: Fix truncating buffer size min_t cast

Greg Kroah-Hartman
2023-09-17T19:38:04Z

From: Kees Cook <keescook@chromium.org>

commit 53e9e33ede37a247d926db5e4a9e56b55204e66c upstream.

If an output buffer size exceeded U16_MAX, the min_t(u16, ...) cast in
copy_data() was causing writes to truncate. This manifested as output
bytes being skipped, seen as %NUL bytes in pstore dumps when the available
record size was larger than 65536. Fix the cast to no longer truncate
the calculation.

Cc: Petr Mladek <pmladek@suse.com>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: John Ogness <john.ogness@linutronix.de>
Reported-by: Vijay Balakrishna <vijayb@linux.microsoft.com>
Link: https://lore.kernel.org/lkml/d8bb1ec7-a4c5-43a2-9de0-9643a70b899f@linux.microsoft.com/
Fixes: b6cf8b3f3312 ("printk: add lockless ringbuffer")
Cc: stable@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Tested-by: Vijay Balakrishna <vijayb@linux.microsoft.com>
Tested-by: Guilherme G. Piccoli <gpiccoli@igalia.com> # Steam Deck
Reviewed-by: Tyler Hicks (Microsoft) <code@tyhicks.com>
Tested-by: Tyler Hicks (Microsoft) <code@tyhicks.com>
Reviewed-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20230811054528.never.165-kees@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
kernel/printk/printk_ringbuffer.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/printk/printk_ringbuffer.c
+++ b/kernel/printk/printk_ringbuffer.c
@@ -1726,7 +1726,7 @@ static bool copy_data(struct prb_data_ri
if (!buf || !buf_size)
return true;

- data_size = min_t(u16, buf_size, len);
+ data_size = min_t(unsigned int, buf_size, len);

memcpy(&buf[0], data, data_size); /* LMM(copy_data:A) */
return true;